• Journal of Mechanical Science and Technology
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• 제17권12호
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• pp.1986-1993
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• 2003

The spatially resolved spray volume fractions from both line-of-sight data of direct measuring cells and a laser diffraction particle analyzer (LDPA) are tomographically reconstructed by the Convolution Fourier transformation, respectively. Asymmetric sprays generated from a twin-hole injector are tested with 12 equiangular projections of measurements. For each projection angle, a line-of-sight integrated injection rate was measured using a direct sampling method and also a liquid volume fraction from a set of line-of-sight Fraunhofer diffraction measurements was measured using a light extinction method. Interpolated data between the projection angles effectively increase the number of projections, significantly enhancing the signal-to-noise level in the reconstructed data. The reconstructed volume fractions from the direct sampling cells were used as reference data for evaluating the accuracy of the volume fractions from the LDPA.

• 한국연소학회지
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• 제8권3호
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• pp.24-30
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• 2003

A convolution algorithm combined with Fourier transformation has been applied to the tomographic reconstruction of asymmetric soot structure to identify the local soot volume fraction distribution. Line-of-sight integrated data from light extinction measurement with multi-angular scanning formed basic information for the deconvolution. Multi-peak following interpolation technique was applied to obtain the effect of increasing number of scanning angles. Height-by-height reconstructed soot volume fraction distribution was compared with laser-induced incandescence signals.

• 전자공학회논문지D
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• 제35D권8호
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• pp.53-61
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• 1998

Dynamic characteristics of widely tunable SGDBR/SSGDBR laser diodes integrated with an electroabsorption modulator is inestigated using an improved large-signal timef-domain model. First, wide tunning properties of a SGDBR laser diode and a SSGDBR laser diode are analyzed respectively and compared with each other. And, intensity-modulation characteristics of a SGDBR laser diode incorprating an electroabsorption modulator are investigated. It is shown that an external modulation has the lower frequency chirp by 1/20 for almost same extinction ratios than a direct modulation, and a nearly transform-limited pulse train can be generated using the optical gating of an electroabsorption modulator.

• 한국가시화정보학회지
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• 제3권2호
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• pp.3-13
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• 2005

The optical patterantor provides the high resolution and quantitative information of the spray. Fuel distribution and Sauter Mean Diameter (SMD) can be measured from fluorescence and Mie-scat-tering images. To correct the attenuation of the laser beam and signal in dense spray region, the method to find the geometric mean of the signal intensities obtained from two cameras was evaluated and verified in a solid-cone spray. In high pressure environment, the increased number density of the droplets cause multiple scattering. The optical patternation technique using a laser beam instead of a laser sheet was applied to minimize the multiple scattering problem. The pattern of a coaxial spray was changed from hollow-cone to solid-cone shape, and the spray angle was reduced as the ambient pressure increased from 0.1 to 4.0 MPa.

• 대한의용생체공학회:의공학회지
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• 제16권1호
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• pp.67-76
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• 1995

Explosive evaporative removal process of biological tissue by absorption of a CW laser has been simulated by using gelatin and a multimode Nd: YAG laser. Because the point of maximun temperature of laser-irradiated gelatin exists below the surface due to surface cooling, evaporation at the boiling temperature is made explosively from below the surface. The important parameters of this process are the conduction loss to laser power absorption (defined as the conduction-to-laser power parameter, Nk), the convection heat transfer at the surface to conduction loss (defined as Bi), dimensionless extinction coefficient (defined as BrJ, and dimensionless irradiation time (defined as Fo). Dependence of Fo on Nk and Bi has been observed by experiment, and the results have been compared with the numerical results obtained by solving a 2-dimensional conduction equation. Fo and explosion depth (from the surface to the point of maximun temperature) are increased when Nk and Bi are increased. To find out the minimum laser power for explosive evaporative removal process, steady state analysis has been also made. The limit of Nk to induce evaporative removal, which is proportional to the inverse of the laser power, has been obtained.

• 한국광학회지
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• 제32권3호
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• pp.120-125
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• 2021

본 연구에서는 다파장 빔결합을 위한 master oscillator power amplifier (MOPA) 구조의 선편광 고출력 이터븀 첨가 광섬유 레이저를 개발하였다. 유도 브릴루앙 산란(stimulated Brillouin scattering, SBS)을 억제하기 위하여 pseudo-random binary sequence (PRBS) 신호로 위상 변조 및 비트길이를 최적화한 선폭 약 10 GHz의 시드 레이저를 구현하였으며, 이를 이용하여 3단 증폭을 하였다. 주 증폭단에서는 모드 불안정성 현상(mode instability, MI)의 문턱값을 높이기 위하여 코어 및 클래딩의 직경이 각각 20 ㎛, 40 ㎛인 편광유지(polarization maintaining, PM) 이터븀 첨가 광섬유를 이용하고 지름이 약 9-12 cm인 나선형 홈에 적용하였다. 그 결과, 입사된 여기광 대비 기울기 효율이 83.7%인 1.004 kW의 레이저 출력을 얻었다. 또한, 빔품질(M²)과 편광소광율(polarization extinction ratio, PER)은 각각 1.12와 21.5 dB로 측정되었다. 더욱이, 역방향 스펙트럼의 레일리 신호와 SBS 신호의 첨두 세기 비율은 2.36 dB로 관측되어, SBS가 완화된 레이저 구현을 확인하였다. 또한 증폭 출력에 따라 기울기 효율 및 빔품질의 저하가 없어 모드불안정이 발생하지 않음을 확인하였다.

• ETRI Journal
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• 제35권3호
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• pp.459-468
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• 2013

A novel integrated laser, that is, a distributed reflector laser diode integrated with an electroabsorption modulator, is proposed to improve the output efficiency, single-mode stability, and chirp. The proposed laser can be realized using the selective metalorganic vapor phase epitaxy technique (that is, control of the width of the insulating mask), and its fabrication process is almost the same as the conventional electroabsorption modulated laser (EML) process except for the asymmetric coupling coefficient structure along the cavity. For our analysis, an accurate time-domain transfer-matrix-based laser model is developed. Based on this model, we perform steady-state and large-signal analyses. The performances of the proposed laser, such as the output power, extinction ratio, and chirp, are compared with those of the EML. Under 10-Gbps NRZ modulation, we can obtain a 30% higher output power and about 50% lower chirp than the conventional EML. In particular, the simulation results show that the chirp provided by the proposed laser can appear to have a longer wavelength side at the leading edge of the pulse and a shorter wavelength side at the falling edge.

• 한국광학회지
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• 제23권5호
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• pp.197-202
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• 2012

맴핑용 레이저 레이더 실험실 시제품의 성능시험과 분석 결과를 소개한다. 광섬유 레이저와 아발란치 광검출기 외 관련 구성모듈로 이루어진 레이저 레이더 시스템이 설계, 제작되었다. 레이저 레이더 시스템은 현재 실험실 환경에서의 성능 확인을 목적으로 하는 실험실 시제품으로서, 레이저 레이더 광원 특성, 거리 정확도, 소광율, 오경보율과 같은 시스템 성능변수가 실험적으로 측정되었다. 실험결과 분석을 통해 레이저 레이더 시제품이 양호한 성능수준을 제시하는 것으로 확인되었다.

• Journal of the Optical Society of Korea
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• 제15권3호
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• pp.227-231
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• 2011

An external optical modulation using absorption s in a Fabry-Perot laser diode (FP-LD), has been proposed and experimentally demonstrated for multicasting in a WDM-PON. The center wavelengths of absorption s in an FP-LD move to short-wavelength rapidly by only a small current (~1 mA) injection. If the current injection is stopped, the s move back to the original position. Such a movement of the s can make the FP-LD act as an external optical modulator, which is found to modulate at a maximum modulation speed of 800 Mbps or more. For a multicasting transmitter in a WDM-PON, the proposed modulator can be cost-effectively applied to a multi-wavelength laser source with the same periodicity of the longitudinal mode. Instead of the multi-wavelength laser source, tunable-LDs are used for experiments. The 32 channel multicasting system with the proposed modulator has been demonstrated, showing power penalties of 1.53~4.15 dB at a bit error rate of $10^{-9}$ with extinction ratios better than 14.5 dB at 622 Mbps.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제25회 KOSCI SYMPOSIUM 논문집
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• pp.113-121
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• 2002

The distribution of volume fraction, mean diameter and number density of soot particles are measured quantitatively in a co-flow ethylene diffusion flame using a simultaneous LII/LIS measurement technique. The LII/LIS system and the measured values are, respectively, calibrated and evaluated by comparing to the informations obtained from laser light. extinction/scattering experiments, LII signal shows some sensitivity to the laser light intensity when laser power density exceeds a certain value(threshold). It is also found that there is an optimal laser intensity and a delay time in order to obtain the best result using the simultaneous LII/LIS measurement technique.